Hi guys,
After discussing mufflers and exhausts with others on the forum. SR20Datsun and I would like to see who else can contribute to an online DIY muffler building and technical thread. I will put up some pics later to make it more interesting.
Basically, I'm on a quest to create the quietest 3'' straight through muffler for a (in my case a 1600) datsun. This isn't about ''putting up with the noise'' because i already do that, this is about ideas and development! Hopefully we can come up with something that the main manufactures don't offer.
To get things going, I have a S13 SR20DET motor. Initially I ran a 3.5'' dump pipe to a 3'' straight through exhaust with a high flow catalytic converter and a 3'' supercat muffler. All stainless.
I want to limit the annoying low frequency waves created as they are the ones that are most frustrating to me. I think they are below 200hz?
Over the years, I've necked the pipe size down with mild steel to 2.5'' from the gearbox crossmember to the rear to reduce noise. However, I've discovered that this does not eliminate the very low frequency waves that are present that a typical OEM chambered muffler reduces through reflective sound cancellation. Which is restrictive.
I've experimented with two different sized hotdogs/resonators. Both 4'' diameter and 3'' exhaust size. One 350mm, the other 600mm long (very tight fit).
I'm now using a Hi-tech muffler (packed with 2kg of long stand fibreglass). I then cut the guts out of it and made the perforated tube into a pronounced 's' shape to slow the gases down and try and absorb some more noise.
I also changed from a 3'' to 2.5'' tip.
My findings:
The 2.5'' center pipe lowered the overall volume but the low frequencies still remain and dominate the interior volume. Cruising seems ok.
Both the hotdogs removed more high frequency waves and gave the exhaust note a 'deeper sound'. Could be just my hearing but this appeared to amplify the lower frequencies.
Changing to a 2.5'' tip reduced the lower frequencies a bit and made the exhaust sound more 'throaty' (which was done at the same time as adding the 's' into the muffler).
I've heard that rockwool packing is better at absorbing sound because it is denser, but also has a 'break in period' because it also takes on water and loses its effectiveness.
A 1/4 wavelength resonator will cancel out a particular frequency and a bit either side, unfortunately the length is too long to place it on the car for the given frequency.
I've also looked at the HKS Super Turbo's slotted tail design (and i really line the sound of this muffler anyway but it's too big for the space available) which they claim eliminates lower frequencies though equalizing sound pressure though the slotted tip. However their tips on this muffler are 5'' in diameter.
Twin tip mufflers seem to be quieter also.
I am considering making the following:
Make a muffler like a twin tip, that divorces one main pipe into two 2'' pipes within the muffler case then join them back to a single outlet. This will equal an area slightly smaller than a 3'' for flow, but will hopefully double the sound absorptive abilities and having a smaller pipe size will also lower the lower frequencies. Then wrap with ss wool and pack it with rockwool insulation.
Attachment:
![[ attachment ]](./download/file.php?id=33558&t=1&sid=d95189f6035b9241dd95c3a9f5d13157)
Muffler 2.jpg [ 44.42 KiB | Viewed 9641 times ]
Thoughts?
_________________
Ongoing Project: 1972 Datsun 510 S13 SR20Det.
http://ozdat.com/forum/viewtopic.php?f=33&t=17898
New Daily: D22 Navara (The new workhorse)
Retired 12/2016: MY98 Subaru Impreza RX
Previous Car: Restored Green 1972 Datsun 510, Hot L18
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